Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

Originator's Protocol for Data Acquisition and Analysis

Aliquots of 100-200 mL from 5-8 depths were filtered onto 25 mm Glass Fibre (GF/F) filters, 5µm or 10µm pore size polycarbonate filters (to yield a total, >5µm and >10µm size fraction, respectively and therefore by difference a <5 and <10 µm size fraction). All filters were extracted in 90% acetone for 24 h, and chlorophyll-a quantified with a Turner Designs Trilogy fluorometer. Final chlorophyll a concentrations were obtained via dilutions of a solution of pure chlorophyll a (Sigma, UK) in 90% acetone and a solid standard.

Instrumentation Description

Turner Designs Trilogy fluorometer

BODC Data Processing Procedures

Data were submitted via email in an Excel spreadsheet archived under BODC's accession number SOC130148. Sample metadata (Date, CTD cast and depth) were checked against information held in the database. There were a couple of minor depth discrepancies - for cast 35 samples were provided with depths 80 m and 50 m, the logsheets indicate these should be 8 m and 5 m respectively.

The concentration data were provided in micrograms per litre. These units are equivalent to the BODC parameter code units (milligrams per cubic metre) and no unit conversion was applied.

The data were reformatted and loaded in BODC's samples database under Oracle Relational Database Management System. Data were marked up with BODC parameter codes and loaded into the database.

A parameter mapping table is provided below;

Originator's Parameter

Units

Description

BODC Parameter Code

Units

Comments

Chl-a (total)

µg l -1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >GF/F phase] by filtration, acetone extraction and fluorometry

CPHLFLP1

mg m -3

n/a

Chl-a (>5)

µg l -1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >5µm phase] by filtration, acetone extraction and fluorometry

SCHLFLPA

mg m -3

n/a

Chl-a (>10)

µg l -1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate >10µm phase] by filtration, acetone extraction and fluorometry

SCHLFLPO

mg m -3

n/a

Chl-a (<5)

µg l -1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate GF/F-5µm phase] by filtration, acetone extraction and fluorometry

SCHLFLPM

mg m -3

n/a

Data Quality Report

There were no comments provided on the data quality.

Problem Report

The overall aim of this theme is to obtain a quantitative understanding of the impact of ocean acidification (OA) on the surface ocean biology and ecosystem and on the role of the surface ocean within the overall Earth System.

The aims of the theme are:

To ascertain the impact of OA on planktonic organisms (in terms of physiological impacts, morphology, population abundances and community composition).

To quantify the impacts of OA on biogeochemical processes affecting the ocean carbon cycle (both directly and indirectly, such as via availability of bio-limiting nutrients).

To quantify the impacts of OA on the air-sea flux of climate active gases (DMS and N2O in particular).

The main consortium activities will consist of in-situ measurements on three dedicated cruises, as well as on-deck bioassay experiments probing the response of the in-situ community to elevated CO2. Most of the planned work will be carried out on the three cruises to locations with strong gradients in seawater carbon chemistry and pH; the Arctic Ocean, around the British Isles and the Southern Ocean.

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.